A bending portion which is operated to bend is provided in an insertion portion of an endoscope. In a bending tube of this bending portion, a plurality of cylindrical bending parts are coaxially provided side by side with each other, and the adjacent two bending parts are swingably coupled by a pair of coupling portions located symmetrically with respect to a central axis. For example, tongue piece portions are provided to protrude on both end faces of the bending part, and the tongue piece portions of the adjacent bending parts are made to overlap one other and then rotatably riveted to each another, thereby forming the coupling portions.
Jpn. Pat. Appln. KOKAI Publication No. 7-128599 has disclosed that, in order to improve the assemblability of the bending tube, a steel ball is interposed between the two tongue piece portions overlapping one another instead of being riveted, thereby forming a coupling portion.